=(1+2(cos10)^2-1)/(2*2sin10cos10)-2sin10(cos5/sin5-sin5/cos5)=cos10/2sin10-2sin10((cos5)^2-(sin5)^2)/(sin5cos5)=cos10/2sin10-2sin10cos10/(sin10/2)=cos10/2sin10-2cos10
